Habitat Fragmentation and Birds

The
landscape of North Carolina has changed dramatically since the first European
settlers arrived over 400 years ago.Thousands of acres of bottomland hardwoods along major river systems,
vast longleaf savannas, shrub-like pocosins, open oak-hickory forests, cove,
northern hardwood, open pine and spruce-fir systems in the mountains and even
large prairies greeted early explorers.All of these areas held a great diversity of birds and other
wildlife.Natural fires and frequent
burning by Native Americans helped create a mosaic of open areas of all types
and sizes interspersed within large tracts of woodlands throughout the state.

As
Europeans settled the state in the 17th and 18th
centuries, the natural landscape began to change drastically.Vast tracts of land were cleared to provide
lumber for homes and ships, start farming operations or create livestock
grazing ranges.This broke up the
continuity of many of our natural systems.As the population of North Carolina grew and expanded, more habitats
were permanently cleared or altered.Extensive logging operations that were not done in a sustainable manner
cleared huge amounts of cypress-gum swamps, bottomland hardwoods and longleaf
pine savannas.Fire suppression in the
20th century greatly reduced and altered many other natural
communities.Many wetland systems were
drained and filled to support farming, pine plantations, new towns and other
development.

As
a result of all these land-altering events, many habitats in North Carolina
today are highly fragmented.This means
they have become isolated into smaller pieces and often no longer function in
an ecologically sound manner for many species of birds.Forests, shrubland and grasslands are now
often broken up into distinct, smaller units that no longer meet the needs of
many migratory or even resident birds.They are separated by large agricultural operations, sprawling towns and
cities, roads, housing developments and shopping malls.Some species of wildlife thrive in these situations.Many do not.Neotropical migratory birds in particular seem sensitive to these
smaller patches of habitat in which they are forced to nest and raise
young.These are the birds that nest in
North America, but spend our winter in Mexico, the Caribbean, and Central and
South America.

Habitat
fragmentation reduces the size of patches of forest, shrubland, wetlands and
grasslands.This reduces the total area
of contiguous habitat available to birds and increases the isolation of the
habitat.It also leads to an increase in
edge habitat that is successfully exploited by a variety of predators that
eat bird eggs and young.An edge is
basically where two different habitat types meet, and in agricultural, suburban
and even rural areas this edge is often very abrupt.Opportunistic and adaptable animals operate
well in fragmented habitats such as raccoons, foxes, skunks, opossums,
squirrels, rat snakes, crows, bluejays, grackles and feral and pet dogs and
cats. They all impact bird populations by eating eggs, young birds and even
adults.Other non-native birds like
European Starlings common in urban and suburban areas compete with native
cavity nesting birds for nest sites.Brown-headed Cowbirds parasitize some birds in fragmented habitats by
laying their own eggs in the nests of other birds (see the fact sheet on
cowbirds for more information).Non-native invasive plants like Japanese honeysuckle (Lonicera japonica), Chinese privet (Ligustrum sinense) and Japanese grass (Microstegium vimineum) encroach into
smaller habitat fragments, limiting the growth of native plants, disrupting
natural succession and limiting vegetative and structural diversity. This in
turn impacts bird populations.

All
of these problems together along with direct loss of habitat can put
considerable pressure on landbird populations in our state and throughout the
region.Overall in the southeast,
predation seems to be the primary cause of bird nest failure, especially among
neotropical migrants.Birds forced to
compete for nesting sites in smaller and smaller fragments of habitat cause
some to raise young in undesirable locations with reduced food supplies or even
abandon nesting efforts altogether.These same problems are also occurring not only in breeding habitats,
but also in migration stopover sites and wintering areas throughout the
Americas for migratory landbirds.Characteristics of the surrounding landscape often influence affects of
habitat fragmentation on bird populations.

Following is a list of scientific papers to help you learn
more about fragmentation of forests, shrubland, grasslands or other habitat
types and the associated impacts on birds:

Marzluff,
J.M. and K. Ewing. 2001. Restoration of fragmented landscapes for the
conservation of birds: A general framework and specific recommendations for
urbanizing landscapes. Restoration Ecology 9:280-292.

Matlock,
G.R. 1993. Microenvironment variation within and among forest edge sites in the
eastern United States. Biological Conservation 66:185-194.